When I first started my writing journey, I bought numerous books on the subject. One thing they all agreed on was the concept of "writing what you know." Did this mean I needed to trash my fantasy novel involving parallel universes? I'm not a student of quantum physics and the mechanics of my world were pulled from my warped brain. Was my story less since I was writing about things foreign to me?
Of course not. I don't believe in "write what you know." I support the idea of "writing from you heart." In other words, write about things you love. In the case of novel writing, you will be working on your project for at least six months to a year, so the subject matter should be something you find interesting and are passionate about or you run the risk of losing interest. For example, someone who loathes world building probably shouldn't write a fantasy novel set in a make believe world.
My stories tend to be more character driven, with the plot being secondary. In the past, I've abandoned projects when I couldn't love the main character. It is hard to spend time with characters you don't care about and sometimes come to detest. The characters who capture my affection are flawed yet still strong. The main character of the series I'm working on is an angry woman who is searching for the truth. I love the sensitive side of her nature and how it balances with angst she feels.
The best advice I can give to new writers attempting to write their first novel is to make sure they love their story. Write from your heart. Tap into your feelings and use what you have experienced to bring your characters to life. You don't need to have fought dragons to write about them, but make sure you have tackled adversity and can relate to the emotions involved with slaying monsters.